1. Field of the Invention
This invention generally relates to communication systems utilizing a satellite link and, in particular, to a method and apparatus for dynamically assigning a satellite link to a client in response to a request from the client.
2. Description of the Related Art
Because of the limited bandwidth of a network of the Internet, especially a limited bandwidth of a line to a home of an Internet user who uses a dial up, users complaints have increased due to unavailability of satisfactory service while the demand of the Internet has consistently increased. A problem for a user who has a dedicated line is inability of assuring enough bandwidth because the user may want to suppress line cost investments to a minimum.
Further, a contents provider tends to demand transmission of a larger data size than conventional information, such as an image and a voice, to make the contents fancier or to provide a new service. This causes the network bandwidth needed by users to expand more and more.
In such circumstance, a satellite network providing an advantage of a wider bandwidth and service area has been focused as a new infra-structure of network. However, a user usually prepares a receive-only device for satellite wave with no transmission function (satellite receiving antenna, antenna adapter or board, set-top-box, etc.) as a user side facility. This means the end-user having only the above receive-only device cannot use a satellite network as a part of the Internet because a bi-directional link which provides on-demand communication is its prerequisite. Therefore, some mechanism has to be implemented into a client machine to make the satellite link appear as if it is bi-directional.
When an end-user""s terminal which does not have a transmitting set communicates with a satellite, the following four schemes a-d may be conventionally available.
a. In this scheme, a client machine simply receives data flowing down from a satellite. This is analogous to the morphology of a television broadcasting and has no on-demand capability which is the basic requirement of the Internet. However, the configuration is simplest. This may be referred to as a xe2x80x9cunidirectional communication receiverxe2x80x9d.
b. In this scheme, a client machine dials up a predetermined site using an inexpensive modem and a telephone line to request transmission of only the data residing in the site server. This is relatively easy to configure and useful, for example, when it is desired to use a satellite network as a part of an intranet. However, this can not be used in a wide area network such as the Internet. This may be referred to as a xe2x80x9csite local receiverxe2x80x9d.
c. In this scheme, a client machine dials up a predefined site in a manner similar to the above scheme b and requests a mediate agent server (proxy server) in that site to distribute data. The agent server receives data from a target server which may be located in other than the dialed up site and distributes it via a satellite. This makes the receiver pretend to do a bi-directional satellite communication in effect though the receiver communicates with the target server indirectly. This morphology can be used not only in a closed environment such as an intranet but also for an Internet service. However, available services are limited because the request from a client depends on service items which the agent server can process. In addition, as well as a site local receiver, the client must connect to a predefined dial-up site first. Also, a client""s request packet must go through the dial-up site regardless of the target server location. This configuration may bring an unwilling state to the customer due to unneeded roundabout. This may be referred to as an xe2x80x9cindirect receiverxe2x80x9d.
d. This scheme emulates a perfect bi-directional communication in which a client transmits a request directly to a target server by using its surface line as a pseudo-transmitting (uploading) channel toward a satellite, while a modem, a terminal adapter (TA) and a telephone line are also required in the manner similar to the above schemes b and c. This may be referred to as a xe2x80x9cbi-directional communication emulation receiverxe2x80x9d. This is also used in this invention and will be described later in detail.
It is necessary to adopt the above scheme d in order to utilize a satellite link as a part of a general high bandwidth network which can be inter-operated with the Internet by making the link pretend to be a bi-directional link, i.e., to utilize a satellite communication as a perfect IP (Internet Protocol) network infra structure.
1. Prerequisite of Client:
A user prepares a client machine having a modem or TA connected with a telephone line to provide a bi-directional link interface (hereinafter called BDL-IF) for a terrestrial link and a receive-only a satellite receiver board, or a satellite receiver having a BDL-IF and an antenna connection interface (hereinafter collectively called xe2x80x9cclient machinexe2x80x9d). To set up the client machine, not only an IP address of BDL-IF but an IP address of a unidirectional interface (hereinafter called UDL-IF), which is different from the one for BDL-IF, must be assigned. This UDL IP address is assigned from a satellite communication provider (hereinafter simply referred to as a service provider which is different from a so-called Internet service provider or ISP) such as a satellite communication enterprise or a satellite communication system integrator.
With regard to a routing table for the client machine, UDL-IF must be set to be a default interface for sending an IP packet. By doing this, a normal outgoing IP packet is hooked to be transmitted to the UDL-IF. This is for the purpose of making the TCP/IP layer above the UDL-IF driver pretend to send out its own request packet from the UDL-IF. At this time, because the receive-only UDL-IF can not send out the IP packet, the user selects a BDL-IF for sending out the IP packet instead of the UDL-IF statically or dynamically with some action. While a request packet is sent out from a selected terrestrial line to a target server, the sender address shown therein is the address of the UDL-IF.
To pretend the above mechanism is sending out a packet from UDL-IF, it is a software prerequisite for the client machine to include a function of delivering (hooking) an output IP packet to the data link layer of a preselected BDL-IF at the moment when the IP packet is delivered from the IP layer to the data link layer of the UDL-IF upon sending out the packet from that interface as shown in FIG. 1. This mechanism is implemented in a place between the IP layer and the UDL-IF driver as a part of the function of the data link layer of the UDL-IF.
What has to be satisfied as a network prerequisite is only to assure that the client machine keeps an IP reachability to the target server through a terrestrial line, and it is not necessary to dial up to a predetermined site in the manner in which a unidirectional communication receiver or a site local receiver does.
The system described above need not modify a TCP/IP application which the user uses daily and the hardware/driver of the interface for a terrestrial line equipped in the client. Therefore, it is a substantial merit that modification of a client is minimized.
2. Data Flow:
The client machine sends out a packet which indicates the address of the UDL-IF as a sender to any target server via the BDL-IF. An addressed target server or destination server receives the IP packet and finds the route by itself or from the parent router that the sender IP address is a part of the address range managed by a service provider.
The addressed target server then transfers a reply packet toward a boundary router propagated by the service provider because the route to the sender indicates the site of the service provider, and sends it either to a router to which a satellite wave transmitting device called a xe2x80x9cfeedxe2x80x9d is connected (hereinafter referred to xe2x80x9cfeed routerxe2x80x9d) or directly to the feed if the feed is a router itself. The feed router or the feed transmits this reply packet toward a transponder (satellite) via a satellite signal divider (multiplexor) and the packet is finally delivered to the UDL-IF of the requesting client machine. As such, it is possible to make the satellite link pretend to be a bi-directional link.
Japanese Published Unexamined Patent Application 9-252271 discloses a technique of IP packet communication utilizing a satellite as described in the above. In this technique, when an IP packet indicating a service request is transmitted from a client PC to a server via the ISDN, the IP address of the sender is rewritten from the address of an ISDN card (BDL-IF) to the address of an STTH card (UDL-IF). The server then sends out an IP packet conforming to the request to the STTH card of the client PC via an antenna and a communication satellite with the address of the STTH card as the destined address.
This invention provides a method and apparatus for dynamically assigning a satellite link for efficiently managing the satellite link. One of the problems solved by this invention is that, in configuring the mechanism for making the satellite link pretend to be a bi-directional network as described above, the service provider has to prepare and notify the respective users of IP addresses dedicated to all client machines and each user has to statically set the address individually. This not only leads to a waste of IP addresses but also possibly causes trouble due to an erroneous setting by the user. In addition, it is difficult to protect the IP address from being used erroneously or without authority by a user.
Further, beside registration of a new user, the service provider has to assure that the IP address be returned when a user cancels a contract of a satellite communication service and reassign the address to another user to properly reuse the addresses. In other words, the service provider has to keep a consistent careful management of each IP address and user information. This means, when the number of users increases, it is not only necessary to reserve a tremendous number of addresses but also considerable labor to manage them is required, so it may not be realistic to keep a careful operation.
This is nothing but assuring a bandwidth of usable satellite link continuously and may cause a problem of inability of efficiently utilizing satellite channel resources or quickly conforming to the increase of receiving sites (the number of client machines). In other words, because it is difficult to precisely grasp the usage of the satellite link or suitably estimate a future usage of the satellite link, this may possibly lead to a problem of the resources by allocating an insufficient satellite link (resource) to a user or, conversely, assigning an excessive satellite link.
In addition, even if it is desired to divide the satellite link depending on the user contracts or the kinds of networks for providing expandability of the service or a security consideration rather than having all users (client machines) share a single satellite link, the division of the satellite link must be difficult because it is impossible to assign an optimum satellite link beforehand by grasping all factors including a future plan.
Because of the above problems, it has been considered to be difficult for a satellite communication to be used by consumers (end users) as a part of existing network or a part of the Internet.
It is therefore an object of this invention to provide a method and apparatus for dynamically assigning a satellite link to efficiently manage the satellite link.
It is another object of this invention to allow a huge number of end users to optimally utilize a wide bandwidth satellite link using a satellite receiver which consists of an existing machine and a receive-only satellite board and antenna or a set-top-box to make IP connection through a communication satellite, and to allow a service provider to efficiently control a satellite channel for effectively utilizing a satellite resource.
The present invention solves the above-mentioned problems. Even if the satellite link can be provided with bi-directional capability, the satellite communication service can not be deployed to any type of users unless the above objectives are solved. Therefore, this invention provides a method and apparatus which use a satellite link configuration protocol (hereinafter referred to as SLCP) for generally utilizing the satellite link as a part of the Internet and an enterprise network (intranet).
SLCP is a protocol which allows a tremendous number of satellite communication users (client machines) to be efficiently contained and allows a service provider to dynamically allocate satellite channels provided by the service provider to satellite communication receiving means by assigning suitable satellite link IP addresses corresponding to the respective client machines.
Further, because the client machine state is controlled by a managing server, when a client itself requests to terminate with its interruption of the use of a satellite link or the managing server determines that the client does not use the assigned satellite resource, the assigned IP address is released to reuse the resource to another client. This means SLCP allows only the client who needs the satellite link to communicate satellite network resulting in a efficient use of the resource.
This invention provides in one aspect thereof a method of dynamically allocating a satellite link in a communication system comprising a plurality of clients each provided with a satellite communication receiving means and a network communication means as well as a managing server for allocating an IP address to the satellite communication receiving means of a given client in response to a request sent from the given client via the network.
The steps of this method includes storing unique information of the aforesaid plurality of clients, establishing a link between a given client and the managing server via the network in response to a request from the given client. A satellite link is dynamically allocated to the aforesaid given client by the managing server based on the stored unique information of that given client in response to the request. An IP address corresponding to the allocated satellite link is sent from the managing server to the given client via the network.
Another aspect of this invention is an apparatus for dynamically allocating a satellite link to a client in response to a request sent from the client via a network in a communication system comprising a plurality of clients each provided with a satellite communication receiving means and a network communication means. This apparatus can include structure for storing unique information of the plurality of clients along with an arrangement for establishing a link to a given client via the network in response to a request from the given client Also included is structure for dynamically allocating a satellite link to the given client based on the stored unique information of that given client in response to the request and sending an IP address corresponding to the allocated satellite link to the given client via the network.
As such, costs required by a service provider can be largely reduced and much benefit can be returned to users because allocation of a satellite link is realized in the best form and operation is efficiently done by a centralized management server. It is to be noted that such merit would not be accepted by general users if an existed client machine must be extensively modified.
However, because SLCP according to this invention can be implemented as a function of the data link layer of the satellite receive-only interface, it is a prominent point of SLCP that modification of the client is minimized.